Metal Peroxide Films

ABSTRACT

Disclosed are adhesive coating compositions containing a metal peroxide for producing clear colorless adhesive coatings on substrates, particularly micro particulate substrates. In one preferred embodiment the nanoparticle coatings are chemically active and function at a high level of efficiency due to the high total surface area of the micro particulate substrate. Also disclosed are coated substrates and compositions having nanoparticles bound to a substrate by the coating compositions.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the benefitof any priority from allowed application U.S. Ser. No. 10/826,565 filedApr. 16, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to adhesive coating compositionscontaining a metal peroxide for producing clear colorless adhesivecoatings on substrates, particularly micro particulate substrates. Thecoating composition changes the chemical and physical characteristics ofthe substrate in useful ways in itself and may also be utilized as avehicle for the attachment of nano or micro particles to a substrate,particularly a micro particulate substrate. The coating compositions areuniquely able to adhere nanoparticles to substrates without interferingwith the physical or chemical characteristics of the appliednanoparticles. In one preferred embodiment the nanoparticle coatings arechemically active and function at a high level of efficiency due to thehigh total surface area of the micro particulate substrate.

2. Brief Description of Related Developments

Many attempts have been made to provide coatings for hydrophobicsurfaces, particularly glass substrates.

A number of references relate to the use of titanium peroxides. Ogata etal, U.S. Pat. No. 6,344,277 dated Feb. 5, 2002 and entitled “Coatingmethod of amorphous type titanium peroxide” describes a method forcoating a substrate having a water repellant surface with viscousamorphous type titanium peroxide in the absence of a surface activeagent.

Ogata also provides a description of the state of the art with regard totitanium peroxide coating solutions.

As disclosed in Ogata et al, titanium peroxide coating solutions forfilm formation comprising peroxopolytitanic acid [a polymer ofperoxotitanic acid] are known to the art. These peroxopolytitanic acidsare obtained by adding hydrogen peroxide to a gel or a sol of titaniumoxide hydrate or a mixed dispersion thereof, and then treating themixture at room temperature or heating it at 90 C or less.

As disclosed in Ogata et al., a viscous product can be obtained as ayellow film by adding aqueous hydrogen peroxide to a fine powder oftitanium hydride to prepare a yellow aqueous titanium peroxide solution,and then evaporating water from this yellow aqueous titanium peroxidesolution. However, Ogata describes this product as being stable only inan extremely low concentration and only for a short time. Moreover, athin layer formed from this product on a substrate is easily cracked orpeeled off and the thin layer becomes porous after a high-temperaturecalcination.

However, Ogata discloses that the peroxopolytitanic acid obtained byadding hydrogen peroxide to a gel or a sol of titanium oxide hydrate ora mixed dispersion thereof, and then treating at ordinary temperature orheating it at 90° C. or less, is different from the viscous amorphoustype titanium peroxide of the '277 patent. The product of the '277patent is obtained by adding hydrogen peroxide to titanium oxide hydrateand carrying out the reaction at 15° C. or less. Ogata recognizes thatthe products are significantly different from each other in physicalproperties, particularly viscosity, that the conventional product ispoor in the function as a binder and that it is difficult to form a thinlayer of the material.

H. Ichinose et al., in the Journal Of The Ceramic Society Of Japan,titled “Synthesis Of Peroxo-Modified Anatase Sol From Peroxo-TitanicAcid Solution”, Vol. 104, pages 914-917 (1996), and “PhotocatalyticActivities Of Coating Films Prepared From Peroxotitanic AcidSolution-Derived Anatase Sols”, Vol. 104, No. 8, pages 715-718 (1996),describe a process to put small amounts (0.85% to 1.7%) of various formsor shapes (polymorphs) of titanium dioxide (TiO₂) into aqueous solutionby reaction with hydrogen peroxide. These solutions are called titaniumperoxidases —TiO(OOH)₂. The amorphous titanium dioxide is the ingredientthat results in the film-forming and adhesive characteristics of theproduct. The mixture is composed of equal weights of the amorphous andanatase (crystalline) forms of titanium dioxide, is soluble in water inup to about 2% by weight of the composition and can be applied atambient conditions. It is not, however, clear or colorless.

Photocatalysts such as titanium oxide and zirconium oxide are known tobe effective for decomposing a harmful organic compound or NO_(x) intoharmless substances by irradiation with an actinic radiation such as UVlight. Many such photocatalysts are in the form of fine powder, makingit difficult to recover the catalysts from reaction mixtures.

Tanaka, U.S. Pat. No. 5,658,841 proposes solving this problem by fixingthe powder catalyst to a suitable support with a binder resin. Acomposite catalyst is provided which comprises a substrate, and acatalytic layer supported on the substrate and including 100 parts byweight of particles of a photocatalyst dispersed in 6-32 parts by weightof a matrix of an alkali metal silicate. Illustrative of suitable alkalimetal silicates are sodium silicate, potassium silicate and lithiumsilicate. These silicates may be used by themselves or as a mixture oftwo or more. Water glass is advantageously utilized as the binder.

Ichinose, U.S. Pat. No. 6,429,169 describes a procedure for creating aphoto catalytically active titanyl peroxide solution. Equal parts byweight of anatase TIO₂ particles are suspended in this solution tocreate the photo catalytic effect. For the uniform suspension, Ichinosesuggests employing ultrasonic waves after mechanical agitation.

The sol concentration of Ichinose is usually adjusted to a level of 2.70to about 2.90% or to a level of 1.40 to about 1.60% by dilution withdistilled water. As reported by Ichinose, when the amorphous titaniumperoxide sol is heated to 100° C. or above, it is converted to anatasetitanium oxide sol. After coating on a substrate and drying, theamorphous titanium peroxide sol is heated to 250° C. or above to convertit to anatase titanium oxide.

Unfortunately, Ichinose's amorphous titanium peroxide films are yellowcolored, prohibiting or severely limiting their use in applicationswhere a clear or white coating is desirable or necessary. A seconddisadvantage of the derived products using the Ichinose process is thatthe coating itself is cloudy and opaque. The yellow coloration is due tothe peroxide content of the solution; the turbidity is due to the sizeof the TIO₂ particles in the solution.

U.S. Pat. No. 6,107,241 (Ogata et al.) and U.S. Pat. No. 6,429,169(Ichinose) disclose an anatase titanium oxide sol which is a yellowsuspension made by adding aqueous ammonia or sodium hydroxide to atitanium salt solution, such as titanium tetrachloride, washing andseparating the formed titanium hydroxide, treating the formed titaniumhydroxide with aqueous hydrogen peroxide, and heating the formed stableamorphous titanium peroxide sol having a concentration of about 2.9%,and a yellow color, to a temperature of 100° C. or higher to form ananatase titanium oxide sol.

The amorphous titanium peroxide sol has good bonding strength but poorwettability for substrates and is yellowish in color.

However, even small amounts of ingredients having particle sizes aboveabout 10 nanometers will render the composition opaque andunsatisfactory for use on transparent substrates. Furthermore, thecoating must be applied in the form of several layers or dips to provideadequate bonding. And the end result is that the yellowish color of eachlayer is intensified to produce an unsatisfactory appearance on clearsubstrates. Multiple layers are necessary because the peroxide-formingfilm is very hydrophobic so that the coating composition does not havegood wetting properties and tends to bead, leaving “holidays” oruncoated areas and requiring multiple over layers.

Thus, there are major detriments associated with the use of the adhesivecoatings of the prior art. The titanium peroxide film former is veryhydrophobic and does not wet out to form a continuous film on thesubstrate, necessitating the application of a heavy amount or thicklayer of the composition in order to form a continuous film or covering.The surface tension of the peroxide-containing film is to some degreeovercome by the added thickness and weight of the film but theadditional material usage and the time and labor required for suchapplication makes the use of the product somewhat impractical.

In addition to the wettability problem, the adhesive coating film isformed with difficulty, and is yellowish in color due to the presence ofunreacted titanyl peroxide. This is aggravated if the weight andthickness of film is increased to overcome the surface tension of thetitanyl peroxide solution to form a continuous coating on the substrate.

The transparency and clarity of the coating(s), when applied on a clearsubstrate, is impaired due to the thickness required to overcome the nonwettability of the substrate. The refractive index of the film soproduced and the excessive thickness causes moire patterns and aseemingly rainbow effect when viewed through clear glass.

The titanium peroxy acid (TPA=titanium oxyperoxide=TiO(OOH)₂ solutionhas a yellow coloration that remains in the product even when it ismixed with nanoparticles of anatase. This yellow coloration isobjectionable on clear substrates. It is highly desirable, and necessaryfor many uses, such as in food, medical and hygienic applications, toremove entirely, or to reduce as much as possible, the yellowcoloration, and to provide clear adhesive coatings. For the use ofcoatings over glass, a clear non-yellow coating that matches thetransparency of the glass is desired.

In numerous commercial products, pigment blends are used to create colorand visual effects that aesthetically appeal to consumers. Becausedifferent consumers have different preferences to various visualeffects, a designer's ability to create and control these effects isoften important to the marketability of a product. Often, additives suchas coated mica flakes, metal flakes, and glass flakes have been used inpigment blends to enhance the visual appeal of items such asautomobiles, boats, planes, appliances, signs, painted surfaces,fabrics, and other consumer goods.

Coated mica flakes, for example, are one of the more common additivesused to improve luster and depth of color of paint compositions on cars.Metal flakes, such as aluminum flakes, are another common additive usedto improve the sparkle of paint and coatings.

While the aforementioned additives offer some of the visual effects thattypically appeal to consumers, a need remains for an economical pigmentblend that enables a designer to create and control a broader range ofvisual effects. Moreover, a need always exists for improved ways toenhance the functional properties of paint and coating compositions,such as increased durability, increased travel, improved patterncontrol, and UV screening,

Micro particles provide an attractive substrate for a range of surfacetreatments because of the inverse relationship between the volume of theparticle and its surface area. The positive effects of this relationshipare increased as the size of the particle decreases. Micro particlescomposed of a myriad of substances and of infinite geometricconfigurations are known. Particles having known or regular geometriesare most useful in many applications. Particles such as glass, ceramicor other inorganic spheres with regular geometries and the ability towithstand environmental stresses are known to be useful in many diverseapplications.

In particular, glass microspheres that range in size from 4 to 50microns in diameter provide a very effective delivery mechanism for arange of surface treatments that deliver performance characteristics oraesthetic effects.

Because of the inverse relationship between volume and surface areanoted above (as the volume of the individual glass spheres decreases,the total surface area represented by a mass of glass spheres increasesbecause so many more microspheres can fit in the same volume of space),microspheres maximize the impact or effect of any surface treatmentsapplied to them. In addition, glass is a strong material (with a highervalue than steel on the Moh's Hardness Scale), can typically withstandcrush strengths of 40,000 psi and is virtually inert. The sphericalshape of glass microspheres facilitates their blending with, andincorporation into, other materials and promotes their smoothdispersion.

Glass microspheres can be produced from different materials, dependingupon the application. The most common glass microsphere is made of sodalime glass, but microspheres are also made of barium titanate andboro-silicate glasses. Soda lime glass is relatively inexpensivecompared to higher refractive glasses such as barium titanate. Byapplying this mineral film to the surface of soda lime glass spheres,the refractive index has been measured to have increased from 1.42to >2.0. This discovery allows the RI of the less expensive soda limesphere to be increased in a cost effective manner.

In general, smaller spheres improve impact strength. Larger spheres tendto improve flow properties. Solid glass beads of soda-lime glasstypically have a specific gravity of 2.46 to 2.50 g/cc, a refractiveindex of 1.51 to 1.52, a softening point of 730 0 C, and the appearanceof an odorless white powder.

Microbeads are also used in cosmetic applications. Microspheres ofcalcium aluminum borosilicate are used in cosmetic formulations toprovide a smooth, silky feel and to improve application properties. Thespheres are chemically inert, have very low oil absorption, and arenonporous. These spheres typically have a specific gravity of 0.1 to 1.5g/cc and have a softening point of about 600° C. and a mean diameter of9 to 13μ

Microbeads of glass, polymers or ceramic composition have demonstratedindustrial usefulness both for their chemical and physical properties.

Polymer powders of various configurations may be formed by mechanical,solution and dispersion methods. See U.S. Pat. No. 4,929,400. Adescription appears in Lerman et al., U.S. Pat. No. 3,586,654 and U.S.Pat. No. 4,221,862 and Sowman, U.S. Pat. No. 4,349,456 (which disclosesvarious hollow, blown, expanded, or solid spherical particles, ormicrospheres, of various refractory materials useful, for example, asfillers for plastic composites or the like, have been disclosed,patented or used in the past, e.g. see U.S. Pat. Nos. 2,340,194,3,264,073, 3,273,962, 3,298,842, 3,365,315, 3,380,894, 3,528,809 and3,748,274, British Pat. Nos. 1,122,412 and 1,125,178, French Pat. No.2,047,751, and Belgium Pat. No. 779,967. The particles or microspheresand/or their methods of preparation disclosed in these references haveone or more disadvantages or limitations which have handicapped theircommercialization or restricted their field of application.

Many applications require the modification of the inherentcharacteristics of the microbeads. In some cases, a surface treatmentmay modify the characteristics of the beads and permit the use of themodified beads in new applications. In some instances the beadsthemselves have useful functional or aesthetic characteristics. In otherinstances the beads are used as a carrier for a functionally activematerial placed on its surface.

One of the inherent problems in applying a coating to microbeads ofvarying composition is the inherent hydrophobicity of the beads. Thisprevents or inhibits the use of water based coatings and requires theuse of more sophisticated and environmentally hazardous solvent basedsystems.

It would be desirable to produce a titanium peroxide composition thatcould be applied to surfaces such as glass and dried under ambientconditions to form clear coatings.

It would be of great benefit to the art to provide a coating formicrobeads of varying composition where the coating can be applied byconventional coating or dipping processes, where the coating is aqueousbased and where the coating application takes place under ambientconditions.

It is the object of this invention to produce a clear colorlessinorganic and photocatalytic coating for substrates used in publicplaces such as hospitals, as well as for self cleaning glass.

It is a further object of this invention to provide a binder producthaving particle sizes less than 10 nanometers in diameter.

It is a further object of this invention to provide a binder producthaving particle sizes less than 10 nanometers while providingphoto-catalytic activity.

It is also an object of the present invention to bind nanoparticles ofmetallic oxides and pigments onto glass, ceramic, polymeric and metallicsubstrates.

It is an object of the present invention to provide a simply controlledprocess for the production of nanoparticles of metallic oxides.

It is an object of the present invention to provide coatedmicroparticles, particularly spherical microparticles that may be usedas a carrier for various nanoparticles attached thereto by the coating.

The exact structure of the deposited mineral film after the peroxidereacts or dissipates is not known but it is assumed to be somewhatlinear as the peroxide monomer form has only two reactive groupsattached to it. Both the rutile and anatase crystalline forms have thesame unit structure and are based on the octahedral arrangement of atitanium atom surrounded by six (6) oxygen atoms. It is the anatase formthat results from this process and for some reason, the octahedralarrangement of the anatase form is more congenial to photo catalyticactivity than the rutile form.

SUMMARY OF THE INVENTION

Disclosed is a process for producing a clear, colorless solution of ametal oxy peroxide of the formula MO(OOH)_(x) where x is 2, 3, 4, or 6comprising forming an aqueous solution of a metal peroxide having theformula M(OOH)_(y), where y is 2, 3, 4, or 6 where such solution issubstantially free of other peroxides of the metal, diluting thesolution to a metal peroxide concentration of between about 0.5% andabout 0.85% by weight of the solution at a pH in the range of from about4.0 to about 6.5, heating the solution to boiling for a period of fromabout 1 to about 4 hours, cooling the solution, reheating the solutionto boiling for a period of between about 1 and about 2 hours, coolingthe solution, reheating the solution to boiling until the peroxideconcentration in the solution is in the range of from about 12.5% toabout 25% by weight of the initially present metal peroxide, and coolingthe resulting clear colorless solution.

Also disclosed is a process for producing nanoparticles of a metal ormetal compound of less than 10 nanometers in size. In a firstembodiment, an aqueous comprising forming a solution of the metalperoxide having the formula M(OOH)_(x) where x is 2, 3, 4, or 6 isformed. The solution is diluted to a metal peroxide concentration ofbetween about 0.5% and about 0.85% by weight of the solution at a pH inthe range of from about 4.0 to about 6.5. The solution is heated toboiling for a period of from about 1 to about 4 hours, cooled, reheatedto boiling for a period of between about 1 and about 2 hours, cooled,and reheated to boiling until the peroxide concentration in the solutionis essentially zero. The nanoparticles of metal oxide precipitate andare separated from the supernatant liquid and dried.

In a second embodiment of the process for producing nanoparticles of ametal or metal compound of less than 10 nanometers in size, a metalperoxide having the formula M(OOH).sub.x where x is 2, 3, 4, or 6 isformed. This peroxide is decomposed to form a metal oxy peroxide of theformula MO(OOH)_(x) where x is 2, 3, 4, or 6. The solution of the metaloxy peroxide is diluted to a peroxide concentration of between about0.25% and about 0.425% by weight of the solution at a pH in the range offrom about 4.0 to about 6.5. The solution is heated to boiling for aperiod of from about 1 to about 4 hours, cooled, reheated to boiling fora period of between about 1 and about 2 hours, cooled, and reheated toboiling until the peroxide concentration in the solution is essentiallyzero. The nanoparticles of metal oxide precipitate and are separatedfrom the supernatant liquid and dried.

In one of its embodiments, the present disclosure relates to a novelmethod for producing colorless aqueous inorganic binder compositions,which can be applied to a substrate under ambient conditions to formsubstantially colorless amorphous coatings having strong wettability andadhesion to both hydrophobic and hydrophilic substrates. These coatingsmay be used alone to impart desirable characteristics to the substrateor may be used as an adhesive to attach other materials to thesubstrate.

In another embodiment, the present disclosure relates to substratescoated with a composition that modifies its esthetic and/or functionalproperties.

In another embodiment, the present disclosure relates to compositematerials having finely divided particles of a first substance bonded toa like or unlike substance using the aqueous binder composition as anadhesive. This is a particularly useful material in that all itscomponents are inorganic and able to withstand significant environmentalstresses.

In a further embodiment, the problems associated with prior artamorphous metal peroxide adhesive films are overcome by changes in theadhesive film production process to remove the color prevalent inexisting metal peroxide adhesive films.

In another embodiment, the wettability of metal peroxide coatings isenhanced by the use of a specified wetting agent or combination ofagents, allowing thinner films to be readily applied.

In yet another embodiment of the disclosure clear colorless inorganicbinder solutions are made photo-catalytic by reacting a titanium salt,preferably titanium tetrachloride with hydrogen peroxide underconditions that minimize or eliminate the production of coloredby-products and that limit the size and amount of the titanium dioxideformed in the final product to within a narrow range of concentrationsand particle sizes.

In yet another embodiment of the disclosure a process for producingmetal oxide particles less than 10 nanometers in size is disclosed.

In yet another embodiment of the disclosure a process for producing TiO₂particles less than 10 nanometers in size is provided.

In another embodiment of the disclosed process and products, thenanoparticles of metal oxide are further reacted to producenanoparticles of a metal or a metal salt.

Other embodiments of the invention include enhanced pigments and pigmentblends, architectural and structural coatings providing self cleaningand/or photocatalytic surfaces, catalysts using microparticles bound tovarious substrates using the disclosed solutions, mixed catalysts ofmicroparticles in intimate contact and bound to an inert inexpensivesubstrate, and substrates with varying refractive indices and decorativeand functional coatings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Disclosed is a process for producing colorless inorganic metal peroxideadhesive and coating solutions, the solutions and the combination of thesolutions with various additives, particularly nanoparticles of metalsand metal compounds, especially metal oxides, for coating of substrates,especially microparticle substrates to provide functional and/ordecorative modification of the surface of the substrates.

A process of making a colorless film forming inorganic metal peroxideadhesive involves solving the problems of removing the persistent colorassociated with the presence of metal peroxides while retaining theadhesive or coating functionality of the composition. It has now beendiscovered that the critical parameters in producing a colorless metalperoxide sol having excellent film forming attributes are to 1] provideat least a stoichiometric amount of peroxide to the metal hydroxidesolution used in producing the composition to convert the metalhydroxide; 2] to reduce the peroxide content in the final adhesivebinder solution to between about 0.07% and 0.22%, preferably betweenabout 0.1 to 0.2, most preferably between about 0.11% and 0.17% byweight of the final solution; 3] to maintain the final binder solutionat a pH below 6.5, preferably below 6.0 and 4] to modulate the rate ofconversion of the metal peroxide to the metal oxide during the finalconversion step by controlled heating and cooling steps.

In a preferred embodiment, the valence of the metal used in the process,where the metal may exist in multiple valence states, is the highest ofthe multiple valence states permitted for that metal.

Suitable metals are those of a metal of group II and group III of thePeriodic Table. Useful metals are scandium, yttrium, titanium,zirconium, hafnium, vanadium, iron, lanthanum, palladium, platinum,aluminum selenium, and tin. Metallic elements in the lanthanide seriesare useful. Especially useful are titanium, platinum, selenium, tin,zirconium and hafnium. Most preferred is titanium.

In a preferred embodiment, the conversion of TPA to TiO₂ is modulated bya processing regime comprising at least one cooling step, preferably atleast two cooling steps, interspersed between at least two, preferablythree, boiling steps.

Using at least a stoichiometric amount of peroxide to hydroxideminimizes the formation of insoluble or minimally soluble hydroxy oroxy-peroxides and permits the simple conversion of residual peroxides inthe solution to the critical level thereby removing the color inherentlypresent in the solution when the various metal peroxide species arepresent.

The novel process produces a binder solution that is clear, withoutcoloration, adheres to porous and non-porous, hydrophilic andhydrophobic substrates and is capable of binding finely dividedparticulate substances to a substrate.

The binder solution is a clear colorless inorganic binder composedprimarily of a metal peroxide in aqueous solution in conjunction with anoxide of the metal and what is assumed to be an intermediate species ofmetal peroxide-oxide.

In a preferred embodiment, the metal peroxide is titanium peroxy acid[TPA]. The TPA solution is diluted to a content in the range of fromabout 0.5 to about 0.85 wt. percent of the solution. The dilute TPAsolution is reacted to reduce the peroxide content to an amountsufficient to provide adhesion and film formation and an anatase contentin an amount below a level to cause turbidity. The reaction is believedto form an intermediate, consisting of anatase particles of about 1 to 5nanometers in size with residual peroxide still attached. The peroxidecontent of this species is low enough to prevent yellow coloration.

In a second preferred embodiment, the TPA is reacted to form a bindersolution which contains sufficient titanium dioxide [anatase form] witha particle size less than 5 nanometers to provide increasedphoto-catalytic activity but below the amount that causes turbidity inthe product.

Solubility in water is a requirement of this process and is critical toits efficacy. Metals in Group II and Group III of the Periodic Tablehaving such soluble hydroxides and peroxides are useful in the process.Other metals such as aluminum scandium, cerium, hafnium, lanthanum,platinum, selenium, titanium, tin, vanadium, yttrium, zirconium, iron,and other members of the lanthanide series of elements and other metalswhich can exhibit a +2, +3, +4 or a +6 valence state and can formhydroxide gels are also satisfactory. Of these, aluminum, iron andtitanium are preferred and titanium is most preferred.

Although the following description is set forth in terms of titaniumoxyperoxide films, it should be recognized that any metal ion (ormixture of metal ions) that forms a hydroxide gel can be employed.

A convenient starting material is the chlorinated salt of the metals ofinterest. The metal usually has a valance of either two, four or six andthus a formula of either MCl₂, MCl₄ or MCl₆. If it is unstable, themetallic halide is stabilized in concentrated HCL. This shifts theequilibrium of the reaction with water and preserves the chlorinatedspecies in an aqueous solution. If it is not concentrated with the acid,the metallic chloride tends to react violently with the water and thecarefully modulated chain of reactions of this process could not becontrolled.

The sol or hydroxide that results when the solution is neutralized byadding hydroxide containing solution, such as ammonium, sodium orpotassium hydroxide, will typically have a structure of M(OH)₂ or M(OH)₄although M(OH)₃ and M(OH)₆ are also useful. These hydroxides are reactedwith hydrogen peroxide to produce M(OOH)₂, M(OOH)₃ M(OOH)₄ and M(OOH)₆,the metallic di, tri and tetra and sexta-peroxides. It is preferred thatwhere the metal used exists in several valence states, the reactionconditions and reactants should be chosen to form the peroxide of themetal at its highest valence state.

Hydrogen peroxide is added to the metal hydroxides to convert thesoluble or marginally soluble metal hydroxides to a soluble state as themetal peroxides. The resulting products—soluble metal peroxides—are usedin the further steps of this process. It is preferable that a minimum ofa stoichiometric amount of peroxide is added to the solution to convertall the hydroxide to the metal peroxide.

In some instances, such as when titanium is utilized as the metalliccation, the initial breakdown of the metal peroxide results in asolution that can be dried to produce an amorphous mineral film. Inother instances, such as where iron is the metallic cation, the peroxideis so unstable that the reaction proceeds directly to the production ofnanoparticles of the metal oxide.

Where the peroxide formed is sufficiently stable it may be controllablyreacted by the application of heat to rearrange it to produce a mineralfilm. This mineral film may then be reacted under controlled conditionsto produce nanoparticles of metal oxide with various crystal structuresdepending on the particular metal oxide and the coordination number ofthe metal of the oxide.

In the case of titanium hydroxide formed by neutralization of the tetrachloride, it is important to remove the chloride ions by decanting themarginally soluble sols (hydroxyl compounds) with water and testing withsilver nitrate to assure their absence. The chloride ions and theircationic counterparts, sodium and potassium ions in the respectivesalts, can interfere with photo catalytic and photo chemical activity.

The soluble metal peroxides-free [or with reduced levels depending onthe intended ultimate use of the material] from salts or halides—thatresult from this process are further processed depending on theapplication.

In prior art processes, upon evaporation of the water from the aqueousstate, the metal peroxide forms an amorphous inorganic film. This filmhas certain desirable characteristics but possesses certain commerciallysignificant detriments such as coloration and opacity that haveprevented widespread use. The use of dilute solutions and controlledheat treatment as disclosed herein have removed these detriments.

In many cases, depending on the metal, the amorphous film so formed is asemi conductor and acts as a binder for the nano sized particles of theoxide of the same or different metal.

The film in its own right, with or without the addition of the nanosized particles, can be catalytically active. When catalytically activeparticles are embedded in the peroxide film-forming component, theparticles can be bonded to glass, metal, plastic or ceramic because ofthe reactive peroxide groups that are present in the film-formingcomponent. In certain cases, for example in the case of titaniumdioxide, the combination of the mineral film and the nano particlesenhances or magnifies the photo catalytic or photo chemical effectsdesired.

In one embodiment, these soluble metal peroxides are transformed intonano particles by heating the aqueous solution of the metal peroxide.Decantation and evaporation of water by controlled heating at 100° C.produces a dry powder of these nano sized metal oxides. Unlike prior artprocesses, the process step of reducing the concentration of the metalperoxide prior to transformation allows significantly better control ofthe conversion rate, size and size distribution of the resultingnanoparticles. Furthermore, the produced nanoparticles do notagglomerate as with prior art processes. The nano metal oxides can befurther processed to produce nanoparticles of the metal or of othermetal compounds.

The narrow particle size distribution of the resulting particles is oneof the important benefits of the process.

The particle size increases, and is proportional to, the length of timethe solution is heated unless techniques such as those described hereinare used to minimize the effect of heating on the size distribution. Thegeometrical arrangement of the metal oxide crystal formed depends on thecoordination number of the metal.

Generalized formulas for producing general nano metallic oxides from MX₂and MX.sub.4 metallic salts [equivalent reactions are applicable to MX₃and MX₆ metallic salts] are

1. stabilization of metallic chlorides in concentrated acid:M(X)_(2,4)+H→M(X)_(2,4)/HX solution  [A]neutralization of acid metallic chloride:M(X_(2,4)/HX+(2 or 4)NH₄OH→M(OH)_(2,4)+(2 or 4)NH₄X  [B]addition of hydrogen peroxide to the metallic hydroxide and formation ofmetallic peroxide:M(OH)_(2,4)+(2 or 4)H₂O₂→M(OOH)_(2,4)  [C]formation of nano particles upon heating peroxide solution:M(OOH)_(2,4)+heat→M(O)₆ anatase octahedral polymorphs  [D]M(OOH)_(2,4)+heat→M(O)₄ tetrahedral and planar polymorphs  [E]formation of amorphous films from metal peroxides:M(OOH)_(2,4)→M(O)n]k  [F]

Titanium oxides exist in several forms. The three natural forms oftitanium oxide are rutile (highly crystalline, the octahedral unitsjoined with each other on two edges), anatase (crystalline, but with theoctahedral units joined together with other units on four edges) andbrookite (less crystalline, with the distorted octahedral units joinedon three edges, and amorphous). The titanium oxides are not soluble inwater. The rutile and anatase forms of titanium oxide are photocatalytic, but the anatase form is more so. The brookite form is notphoto catalytic.

Titanium tetrachloride TiCl₄ is a liquid that is rapidly hydrolyzed withwater to produce a white smoke used in sky writing. For use in thepresent process, the material must be stabilized in sufficiently stronghydrochloric acid. It is convenient to use 2N HCl. It is found thatcooling the 2 N HCl to 5° C. before adding the TICl₄ slows down theformation of side reactions as the TiCl₄ dissolves into the acid/water.

The TiCl₄/HCl solution is neutralized with 2 N ammonium hydroxide,NH₄OH, producing titanium tetrachloride, Ti(OH)₄, and ammonium chloride,NH₄Cl.

The NH₄Cl must be removed before addition of the peroxide. This is doneby separation of the Ti(OH)₄ from the NH₄Cl by any convenient separationtechnique such as by the addition of distilled water and separation ofthe precipitated Ti(OH)₄. This process is continued until the chloridecontent as measured by silver nitrate titration is at or below 0.05%concentration of the solution.TiCl₄@5° C. at 0.25 Molar concentration+1 L 2N HCl═TiCl₄/2N HCL aqueoussolution.TiCl₄/2N HCl+2N NH₄OH═Ti(OH)₄+NH₄ClTi(OH)₄+distilled water/phase separation=Ti(OH)₄; Cl content less than0.05%.

In prior art processes, the Ti(OH)₄ will start to dissolve and theseparation becomes more difficult when the chloride concentration isbelow 0.05%. In prior art processes, at least 500 parts/million ofammonia are left in the solution to stabilize the anatase particlesformed later in the process. This causes problems because the particleswill more readily precipitate if ammonium ion is not present. Thepresent process can use much less, e.g. 250 parts/million of ammoniumion, to stabilize the anatase crystals. Thus, the level of chloride ioncan be dropped further using decantation, avoiding the necessity ofusing ion exchange resins to lower the chloride ion content. Sincechloride ion content interferes with the photo-catalytic effect itshould be minimized if such effect is desired after further processing.

In a preferred embodiment, the process begins with the peroxidation oftitanium tetrahydroxide [titanic acid]. The peroxidation reaction yieldsdifferent results depending on the amounts of reactants introduced tothe reaction and on the reaction conditions.

The following equations show the resulting compounds at various ratiosof reactantsTi(OH)₄+1H₂O₂→Ti(OH)₃(OOH)+1H₂O  [1]Ti(OH)₄+2H₂2O₂→Ti(OH)₂(OOH)₂+2H₂O  [2]Ti(OH)₄+3H₂2O₂→Ti(OH)(OOH)₃+3H₂O  [3]Ti(OH)₄+4H₂O₂→Ti(OOH)₄+4H₂O  [8]

Above a ratio of 4 to 1 there are no hydroxyl groups on the titaniumhydroxide Ti(OH)₄ to further react with the peroxide and the addition ofexcess peroxide results in no changes to the final products.

It is critical to the operation of the process and production of theclear metal peroxide film that the reactants and the reaction conditionsare such that the reaction of the hydroxide and the peroxide yieldsessentially only a single metal peroxide. It is preferable that thatmetal peroxide be the peroxide of the metal at its highest valencestate.

Once a TPA solution essentially free of significant quantities of otherperoxide species is obtained, the solution can be further processed toobtain an amorphous film forming binder solution that is clear andcolorless.

The stability of the peroxides decreases as the number of peroxide unitsincrease. Thus, the monoperoxide produced in reaction [1] is more stablethan the diperoxide of reaction [2], etc.

The stability of the titanium tetraperoxide produced by reaction [4] isso low that it must be kept at temperatures below 5° C. to preventdegradation. Above 5° C. the titanium tetraperoxide reacts to formtitanium oxyperoxide [TPA]. [1]

A comparison of the reaction products produced when the ratio ofhydrogen peroxide to titanic acid, Ti(OH)₄, is less than 4 to 1 withthose which occur when the ratio is approximately 4 to 1 is illustrativeof the significant differences between the present process and the priorart processes.

Some TPA will be produced regardless of the reaction and the ratio ofhydrogen peroxide to titanic acid. Thus for example, as utilized by theprior art processes, TDDA produced by reaction [2] can be converted toTPA by the dehydration of titanium dihydroxy diperoxy acid [TDDA]. Thereaction is as follows:Ti(OH)₂(OOH)₂<−>TiO(OOH)₂+H₂O  [6]

Since there is an overwhelming amount of water present the equilibriumis driven to the left and, in water solution TDDA, not TPA, is thedominating species present. Additionally TDDA is a relatively stableperoxide and thus significant heat input is required to first drive offthe water and then decompose the TDDA. Because of the high energy inputrequired it is difficult to control the reactions which causesignificant problems in further processing and with the quality of theproduct obtained.

TDDA yields by-products during the dehydration process [6] of which thefollowing condensation reaction is an example.2Ti(OH)₂(OOH)₂→Ti₂O(OH)₄(OOH)₂  [8]

This is a yellow compound. It is not converted into TPA. At boilingtemperatures it is slowly converted into TiO₂ but crucially, the yellowcolor persists until it is fully converted. It also contributes toopacity and non-clarity of the binder solution.

Another soluble species formed when the ratio of titanium hydroxide tohydrogen peroxide is less than about 4 to 1 is Ti(OH)₃(OOH). It isproduced in small amounts with a 2:1 hydrogen peroxide molar ratio butnot with a 4:1 hydrogen peroxide ratio. It is a stable peroxide and assuch is colored yellow. Ti(OH)3(OOH) is not converted into TPA. Itpersists in the solution until the end point when all the peroxidespresent are converted into anatase. Its presence contributes to a yellowcolored binder solution.

Thus, when TPA is produced from a peroxide other than Ti(OOH)₄ [Eq. 4]other peroxide species are present in the solution, all are yellow incolor, and all persist until all the peroxides are converted to anatase.When all the peroxide is converted to anatase the product becomes white,it loses its film forming capabilities and cannot function as a binder.Prior to the time the peroxides are all converted to anatase, thevarious species remain and the solution remains yellow.

As described above [Eq. 6 the tetraperoxide is the least stable of theperoxy species present in the solution and thus is the first to formTPA. Furthermore its lower stability permits significantly greatercontrol over further processing parameters, in particular when it isused at low concentrations. This is also true of the other metalperoxides.

Thus, unless a procedure can be found where titanium tetraperoxy acid isthe only peroxide compound present in solution it will be impossible toform a clear, colorless solution which retains its adhesivefunctionality.

With TPA as the only peroxide compound present in solution, the peroxidecontent can be reduced by conversion of a majority of the TPA to TiO₂ tothe point where the yellow color is not visible but where a sufficientquantity of the peroxide remains present to allow film formation.

Anatase TiO₂ may be produced from either TPA or from TDDA. The reactionproducing TiO₂ from TPA is as follows:TiO(OOH)₂→TiO₂+H₂O+O₂  [7]

When TDDA is used, it must first be dehydrated to produce TPA [6] andthen in a second step produce anatase.

Furthermore, another crucial aspect of the disclosed process is that therelative instability of the TPA allows conversion to take place underrelatively mild reaction conditions such that the amount of residualperoxide present can be carefully monitored and controlled.

A 2/1 ratio makes the solution less acidic. TDDA is less acidic thanpure TPA. As the peroxide decomposes producing TiO₂ and oxygen, the pHbecomes more alkaline. It is found that pure TPA when being converted byboiling to anatase becomes more alkaline than when the TDDA producedfrom a 2/1 ratio is used. It is important to control the pH so it doesnot rise above a pH of about 6.5 during processing. Preferably the pH ismaintained in the range of from about 4.0 to about 6.0.

There are intermediate steps in the production of the amorphous TiO₂film. At boiling temperature, the peroxide content is dissipated andTiO₂ anatase is produced. However, at ambient temperatures slowcondensation reactions occur that indeed produce a mineral polymermatrix. This is unique in the inorganic world as polymers are usuallycalled crystals and minerals. The amorphous state allows a noncrystalline polymer of film to be produced.

When the TPA is exposed to conditions that cause dehydration of thecompound, a dimer is formed, as follows: dehydration2Ti(O)(OOH)₂→TiO(OOH)—O—TiO(OOH)+H₂O+O₂  [9]

The dimer can again condense as follows:2TiO(OOH)—O—TiO(OOH)→TiO(OOH)—O—TiO—O—TiO—O—Ti(OOH)  [10]

This condensation continues at high temperatures and a polymer isproduced until eventually all the peroxide is gone. Prior to completion,there is residual peroxide present, though at a decreased level, as thecondensation process continues. At a certain level of remainingperoxide, the yellow color disappears.

The disappearance of the yellow color occurs only when the level of allperoxides in the solution are condensed to the critical level. This canonly occur when the starting material is essentially free ofpolymerizable peroxides, e.g. when the peroxides in the startingmaterial are essentially all TPA.

As the condensation proceeds with applied heat a portion of the polymereventually will convert to anatase and no longer be a film former. Thetitanium and the surrounding oxygen atoms become coordinated due to thed-orbitals into octagonal unit structures that assemble into the anatasecrystal structure. This does not occur at temperatures under 100° C.;the amorphous polymer is stable.

It is crucial that the concentration of the TPA in solution be reducedto the level specified to delay the formation of anatase during furtherprocessing of the TPA and to allow a controlled reduction of theperoxide content to achieve a balance of peroxide content with anatase.

The peroxide content remaining in the TPA is reduced to below the yellowcoloration threshold of about 0.22% but is maintained at levelsufficient to allow film formation during further processing.

The anatase produced at this threshold is photo-catalytic. As theperoxide content decreases to about 0.07% the film forming capabilityremains and the photocatalytic capability of the solution increases. Theanatase and peroxide present at this concentration produce a non-yellowand photo-catalytic film upon further processing. Below about 0.07% thefilm forming capability of the solution is lost.

The resulting mixture of anatase and peroxide differs substantially fromthe solution resulting from the mixing of anatase into a solution of TPAas in the prior art procedures that do not remove the yellow color fromthe solution.

The concentration of the peroxide is measured using a dilute 0.01 to0.05 N solution of potassium permanganate in 1 N sulfuric acid.

It has been determined that the colorless range starts with a peroxidereduction of 50% from the original peroxide concentration but not lessthan 25% of the original concentration. In the case of titanium, theconcentration of the TPA in solution is in the range of 0.5% to about0.85% before reaction. Of this about half of the weight of the TPAmolecule is attributable to the peroxide moiety. Thus the peroxideconcentration [as distinguished from the metal peroxide concentration]in the solution prior to reaction is in the range of from about 0.25% toabout 0.43%. Therefore, the solution becomes colorless when the peroxidecontent is reduced to a range of from about 0.07% to about 0.22% by theheating, and cooling cycles described herein. It should be noted thatmerely reducing the peroxide content to this range without following thetemperature cycling procedure does not yield a colorless solution.

An additional advantage of the disclosed process is a clearer solutionand more uniform anatase particle size distribution in the 5 to 10nanometer range. This is important in applications where the coating isapplied to a transparent substrate where large particle sizes produceopacity and turbidity.

The Ti(OH)₄ is cooled to 5° C. Peroxide equal to four times the molarlevel of titanium is cooled to 5° C. and added. The addition of 4 molesof peroxide assures complete reaction to form Ti(OOH)₄. Ti(OOH)₄ is veryyellow and opaque. It is unstable above 5° C. and decomposes to produceTPA water and oxygen.Ti(OH)₄ cooled to 5° C.+H₂O₂ cooled to 5 degrees=Ti(OOH)₄.

The solution gradually becomes transparent as the oxygen is evolved andthe TPA is formed. It is found that the clearer the TPA solutionproduced the clearer will be the final product produced once the TPA isheated for a prolonged period of time.

The concentration of TPA is reduced to a concentration in the range offrom about 0.5% to about 0.85% by weight of the solution [peroxidecontent of 0.25% to about 0.43%] as opposed to the prior art processeswhich disclose 1 to 2 percent concentration.

This low concentration slows the production of anatase crystals andallows the peroxide to convert to TiO₂ at a slower rate than if at ahigher concentration. A window opens that allows the presence of theperoxide and of very fine anatase particles to be present in a usefulratio. For a colorless solution that is photo-catalytic a maximumconcentration of anatase particles with enough peroxide to remain toinsure film formation is desirable.

If all the peroxide is converted, the particle size continues to grow asthe peroxide content is decreased. Eventually the particles sizes becomeso large they are no longer able to remain in solution and precipitate.Small diameter nanoparticles of 1 to 5 nanometer particle size areassured by terminating the reaction while a small peroxide contentremains. The small size gives increased clarity as well as enhancedphoto-catalytic activity.

TiO(OOH)₂ is TPA. The TiO(OOH)₂ is measured using 0.1 or 0.01Npermanganate, in H₂SO₄.

Once the concentration of TPA has been determined a sufficient quantityof distilled water is added to reduce the concentration of the TPA to0.5 to 0.8 weight percent of the solution.

The dilute TPA solution is heated to boiling for a period of from about1 to about 4 hours, preferably from about 2 to about 4 hours. In analternative embodiment it is boiled under reduced pressure, typicallyabout 0.6 atmos. In a critical step, the TPA is cooled to ambienttemperature prior to completion of the heating. The TPA is then againheated to boiling. This cycle is preferably repeated twice until theperoxide content reaches the desired level. The color of yellow fades asthe peroxide content is reduced. When the yellow color disappears, thesolution is cooled and the peroxide content is measured.

To prepare a binder solution, the peroxide content is allowed to fall to¼ to ½ the initial value but no lower. At this level, the yellow hasdisappeared but sufficient peroxide content is available to form a film.Anatase begins to be present at this concentration of peroxide. Itconsists of a fine, less than 10 nanometer size diameter. At this sizethe anatase does not affect the transparency of the solution. Theoptimum balance occurs at a ¼ percent value of the initial peroxidecontent. This assures a high enough level of anatase particles forphoto-catalysis. The resulting solution is a colorless clear solutionsuitable for coating over transparent surfaces.

While not confirmed and without intending to be bound by theexplanation, it is believed that the small size of the anatase particlesis maintained by the presence of an intermediate material consisting ofjoined anatase unit structures in an octahedral array with residualperoxide still attached to the array. This is in effect a small anataseparticle with peroxide still attached. The attached peroxide assures thesmallness since it has not been reacted and caused further anatasegrowth in size.

The non photo-catalytic colorless binder has many applications.

It may be utilized as a binder to bind TiO₂ [rutile form] pigment to avariety of substrates. In particular, it may be utilized as a binder tobind TiO₂ (rutile form] pigment to micron-sized spherical particles,most particularly micro-spheres of glass. Such products can be used toincrease the opacity or other desirable characteristics of coatings orpaints while minimizing the amount of TiO₂ used in the coating or paint.A particularly useful application is in the application of white linesmarking lanes on roads and highways.

The non photo-catalytic colorless binder provides significant benefitsin that it reduces the amount of TiO₂ [rutile form] that must be addedto the coating or paint thereby further increasing the cost. Becauseeven trace amounts of yellow reduce the whiteness and brightness of thecoating and require more rutile pigment to be used, coating a colorlessbinder that adheres the rutile pigment to a substrate requires lessrutile and reduces the cost.

The non photo-catalytic colorless binder is useful as a general binderof micron sized particles to be bonded to ceramic, metal glass andcertain plastics. In particular it is useful as a general pigment binderof pigments to be bonded to various substrates, especially ceramic,metal glass and certain plastics.

The non photo-catalytic colorless binder is useful by itself as aprotective coating for masonry and architectural finishes on theexterior of buildings or other structures.

The non photo-catalytic colorless binder is useful by itself as abarrier coating over painted metal and other surfaces that would beattacked by environmental conditions.

The non photo-catalytic colorless binder is useful by itself as abarrier coating over susceptible substrates or coatings prior to theapplication of a photo-catalytic coating. Thus, for example, where aphotocatalytic coating applied directly over a painted surface mightcause degradation of the paint, the binder would act to minimize theeffect of the photo-catalytic coating. There is significant applicationof the binder as a barrier coating between automotive panels andautomotive self-cleaning [photo-catalytic] coatings.

Where the binder is applied to a glass surface a prime coat of thebinder would block migrating sodium and chloride ions from the glass andthus increase the photo-catalytic efficiency of a photocatalytic coatingapplied over the binder coated glass substrate.

Where the binder is produced with a level of TiO₂ [anatase form] toprovide photocatalytic activity, the coating provided significantbenefits when applied over transparent surfaces such as glass where highlevels of transparency and light transmission are required.

The photo-catalytic colorless binder has many applications. Among itsmany applications may be included anti graffiti sprays; architecturalcoatings; sterilization coatings for hospitals and public gatheringplaces; self-cleaning transparent glass; self-cleaning automotivesurfaces; self-cleaning textiles, i.e. for medical and civilian uses;coating on paper money; water pollution control by means of the surfacetreatment of glass beads as carriers of a photo catalytic coating; thesurface treatment of hollow glass beads for use in oil spills;self-cleaning outdoor carpeting.

In its photocatalytic embodiment, the binder provided significantbenefits as a coating over surfaces where preservation of the underlyingcolors is desired, over white surfaces and light shades where nonyellowing is important, as a hygienic coating where non-yellowing andclarity are important, and as a coating over white porcelain surfacesand ceramic tiles. Preferably, a coating of the non-catalytic embodimentof the coating is added between the painted substrate and thephotocatalytic coating.

The substrate to which the binder is applied may be made of inorganicmaterials such as ceramics, glass and the like, organic materials suchas plastics, rubber, wood, paper and the like, and metals such asaluminum, steels and the like. Organic polymer resin materials, such asacrylonitrile resin, vinyl chloride resin, polycarbonate resins, methylmethacrylate resin (acrylic resins), polyester resins, polyurethaneresins and the like are useful substrates. The substrate is not criticalwith respect to the size or shape and may be in the form of a honeycomb,fibers, a filter sheet, a bead, a foamed body or combinations thereof.If a substrate which allows transmission of UV light is used, aphotocatalytic body may be applied to the inner surface of thesubstrate.

In its catalytic embodiments, other than photocatalytic embodiments, themicrosphere-binder combination can be used as a substrate for nano sizecatalysts such as hydrogenation catalysts, (i.e. palladium, platinum andcadmium oxides), oxidation catalysts (i.e. nickel) and polymerizationcatalysts (i.e. tin and titanium), among others.

Using the binder, a catalytic moiety can be bonded to ceramics, tiles orspheres; to metal substrates such as aluminum; or to glass or to glassceramics.

Coated glass spheres in the under 20 micron size, and even more so atthe 10 micron or under size, allow their incorporation in paints andcoatings where thin applications are required for technical, as well aseconomical reasons. For example, some paints are applied at a thicknessof only 10 microns so coated glass microspheres with larger diameterswould protrude from the resulting film.

As another example, in water purification, coated microspheres could bepacked in large quantities in tubes. When water is then passed throughthese tubes and comes in contact with the coated microspheres, the UVlight source present activates the photocatalytic coating, resulting inthe oxidation of any organic materials present in the water.

This binder solution, in its photocatalytic form, can also be applied tohollow glass beads so that in the case of oil spills, for example, oiland organic materials floating on the water's surface would be oxidizedwhen they came in contact with the coated beads.

Another application of the colorless adhesive solution is as a binderfor pigments of from 1000 nanometers and under to varying substrates,particularly including glass microspheres. The presence of anycoloration in the binder adversely affects the color particularly awhite color where the pigment is rutile titanium dioxide. The removal ofcoloration makes brighter colors in the wave length of the desiredcolor.

An application is as a substrate for pigments or other colorants thatreduces the amount of colorant required to produce the specifiedintensity of color.

The surface treatment of glass microspheres with a metal peroxidesolution, particularly a titanyl peroxide solution, results in creationof a mineral film that adheres to the microspheres. This surfacetreatment can be applied with a brush, by spraying the microspheres or,probably the most effective way, by immersing the microspherescompletely in the titanyl peroxide solution. Upon evaporation of thewater at room temperature or with the application of heat to facilitateevaporation (but not to facilitate formation of anatase particles), theperoxide dissipates and the resulting mineral film bonds to the glassmicrospheres. This film is permanently bonded to the microspheres andwill not dissolve or wash off, even when re-immersed in water.

Where additional binding is required, a wetting agent may be used inconjunction with the binder. However, many wetting agents do notfunction properly in the inventive system. It has been found thatpolyethylene oxide silane wetting agents, of which Dow ChemicalsSilicone Q25211 super wetting agent is a preferred example do notinterfere with the adhesive qualities of the film former yet allow thefilm former to coat the different substrates to which it is applied.

A particularly significant application of the disclosed method ofproducing nano particles from metal compounds that produce stablehydroxides and have a valence of at least two, and are preferablyselected from Fe, Cu, V, Ca, Cr, Co, Pt, Zr, or Nb relates to their usein the field of pigments. There are two important aspects to thisdiscovery.

First, the disclosed production techniques for the production of nanoparticles allow a broader range of nano-sized particles to be utilizedas pigments themselves. While some organic pigments, such as carbonblack, are available in nano size ranges, this process allows inorganicmetal oxides and from them metals and metal compounds to be produced inthe nano size range. These metal oxides are the basis of many colors inthe pigment field. For example, the iron oxides produce red pigments;the cobalt oxides produce blue color; cadmium and chromium oxidesproduce yellow colors. Vanadium dioxide is also a blue pigment.

The second significant discovery relates to the fact that solid orhollow glass microspheres can now be used as carriers of a wide range ofmetal oxide-derived films and nano particles. The mineral film formed byevaporation of the peroxide solution provides an adhesive coating thatallows the nano size particles to be attached to any substrates to whichthe peroxide solution is applied. The inverse relationship betweenvolume and surface area (3/r), where r is the radius of the sphere,results in an increase of the surface area per unit weight of thematerial as the radius and thus the volume of a sphere decrease.

The glass sphere carrier has more surface area to which nano particlesof an even smaller size can be attached while at the same timepreventing agglomeration of the particles. With appropriate sizing ofthe glass spheres and attached particles, surface area can be optimizedfor each application. The overall result is a maximization of exposureof the surface area of the metal oxide, both from their inherent smallsize and from their attachment to the glass micro sphere “carriers”. Theintensity of the color can be increased due to both the small nano scaleof the metal oxide pigments and to the light refraction of these nanosize particles, which occurs as a result of their attachment to theglass spheres. For the same reason, increased catalytic activity can beobtained by attaching catalytic nanoparticles to the glass spheres tomodulate catalytic activity.

Use of glass microspheres as a pigment carrier also impartscharacteristics to the nano pigment that previously might have beenlacking. The glass sphere carrier provides, in many cases, a harder orstronger pigment, may assist in the flowability or dispersion of thepigment in some paints or coatings, and may impart characteristics, suchas infra red reflectance of heat, that are known characteristics ofglass spheres themselves.

In addition to the general category of nano particles with applicationsas pigments, there are other important applications where glass, ceramicor plastic microspheres can be used as the delivery mechanism for othermetal oxides. The coating or surface treatment of glass microsphereswith mineral film and embedded nano size metal oxides such as platinumand nickel oxides could offer significant cost and weight advantagesover current catalytic converter technology used in automobiles. Sincethe film is stable at temperatures up to at least 500° C., it may beused in severe chemical processing environments.

EXAMPLES Example 1 Preparation of Titanium Tetrachloride

A sufficient quantity of concentrated HCl is mixed with distilled waterto form a 2 N HCl solution. The temperature is lowered to 5° C.

Twenty-five [25] ml of a 100% solution of titanium tetrachloride,equivalent to adding 43.15 grams or 0.2274 moles TiCl₄/liter of solutionof TiCl₄, at 5° C. is added per liter of water 2 N HCl solution. Thislow temperature allows the titanium tetrachloride to hydrolyze anddissolve in water without causing side reactions or reacting overvigorously. Too high a temperature can produce opaque materials andinterfere in the next processing steps.

The ratio of TiCl₄ to HCl is preferably about 9 parts HCl to 1 part ofthe TiCl₄. It is possible to have higher concentrations of TiCl₄ butthen the normality of the HCl must also be increased and, during theneutralization process, this produces more NH₄Cl which must be removedby decantation or centrifugation. It is important to reduce the chlorideion to under 0.05% of the solution where the binder is intended to beused with photocatalytic moieties.

Example 2 Preparation of Titanium Hydroxide

While maintaining the reactants at a temperature of 5° C., a sufficientquantity of 2 N ammonium hydroxide is slowly added to the HCl/TiCl₄solution to neutralize the acid from the 2N HCl and from the 0.2274moles of TiCl₄ which produces 0.9097 moles of acid/L in addition to theHCl present from the HCl solution.

The resultant titanium hydroxide is produced in the form of a whiteprecipitate sol. This sol is repeatedly washed (decanted) in aseparatory funnel until the percent chlorine is reduced to no more than0.05% by weight of the solution as measured using the Mohr method(silver nitrate titration).

As the chloride content approaches the 0.05% level the solution startsto turn white and cloudy due to Ti(OH)₄ re-dissolving in the chloridefree solution.

High levels of chloride ion prevent the Ti(OH)₄ from re-dissolving inthe water. The competing equilibriums of ammonium chloride ions insolution with Ti(OH)₄ molecules drives the reaction and prevents theTi(OH)₄ from re-dissolving.

The Ti(OH)₄ produced is dried and weighed. A yield of 26.35 grams/l ofTi(OH)₄ is recovered from the 43.15 grams of TiCl₄/l initially present.

Example 3 Preparation of TPA

A 30 percent hydrogen peroxide solution is chilled to 5° C. and addeddrip wise over a time period of 15 minutes to the chilled solution ofTi(OH)₄ containing less than 0.05% chloride ion.

The total amount of hydrogen peroxide added is equivalent to 4 times themolar amount of the titanium hydroxide present or 0.9097 moles/L,equivalent to 30.92 grams of 100% hydrogen peroxide per liter. At a 30percent concentration this is 106.25 grams H₂O₂ per liter of Ti(OH)₄solution.

The reaction of the H₂O₂ and Ti(OH)₄ produces TPA. The concentration ofthe TPA is reduced by adding sufficient distilled water to lower theconcentration to 20.45 grams per liter, equivalent to 0.1574 moles ofTPA per liter equal to a concentration of TPA of 2.045% by weight of thesolution as determined by titration against permanganate.

Example 4 Preparation of Clear, Colorless Binder Solution

The TPA produced in Example 3, at an original concentration of 2.045%and diluted to a concentration of 0.65% [peroxide content of 0.327%] isheated to a temperature of 100° C. for a period of 3 hours. The solutionis then cooled to room temperature for an hour and then heated toboiling. Heating proceeds for another 2 hours and then the product iscooled again at room temperature for one hour and reheated to boiling athird time.

After cooling, it is tested to determine the final peroxide content bytitration against permanganate and the amount of peroxide is measured bycalculating the amount of permanganate consumed indicated by an endpoint of a permanent purple color due to unreacted permanganate. Thefinal peroxide concentration was 0.15%.

Example 5 Preparation of Photo-Catalytic, Clear, Colorless BinderSolution

The TPA produced in Example 3, diluted to a concentration of 0.65 wt %[0.327% peroxide] is heated to 100° C. for a period of 3 hours and thecooled to room temperature for 1 hour before heating to boiling for 2hours and again cooled to room temperature for 1 hour. It is heated toboiling a third time until the peroxide content reaches 0.10%. It istested to determine the final peroxide content by titration againstpermanganate and the amount of peroxide is measured by calculating theamount of permanganate consumed. The final peroxide concentration wasbetween 0.11% by weight of the total solution The solution was clear andcolorless in appearance.

Exemplary techniques for preparing coated substrates are as follows:

Example 6 Preparation of Coated Microspheres

Soda lime glass spheres (PS 1011) obtained from Potters Industries, Inc.having a refractive index of 1.54 as determined using standardizedrefractive index liquids and having a diameter of between 4 to 20microns are prepared for coating by placing them in a beaker equippedwith a magnetic stirrer and a heating mantel. The distribution curve ofthe spheres is Gaussian, as described by a normal distribution curve.

The beads are washed with about 15% of their weight of isopropyl alcoholand removed from the alcohol. One hundred grams of the washed beads and153.84 grams of the solution of Example 4 was added to the glass in acoating vessel. A batch stirrer was used to constantly mix and stir thebeads.

To assist the wetting of the beads, 20% of the weight of the glass beadsof isopropanol and a wetting agent, polyethylene oxide silane, in anamount equal to 5% of the weight of the binder solution was added to thebeads in the coating vessel.

The beads were heated to a temperature of 80° C. for a period of about 3hours to evaporate the liquid. The coated beads were removed from thevessel when they were dry. The refractive index of the free flowingcoated beads was determined by the method specified above and was foundto be at least 2.0.

Example 7

Alternative Drying Technique

The procedure of example 4 was followed except that an alternativedrying technique using vacuum distillation and low temperatures isutilized where the boiling temperature is reduced with a vacuum. Thebeads were heated in a vacuum chamber at a pressure of 0.6 atm and at atemperature of about 80° C. until dry, approximately 1 hour, toevaporate the liquid.

The coated beads, containing a clear and colorless, adherent film, areremoved from the vessel when they are dry. The refractive index of thefree flowing coated beads is determined by the method specified aboveand is found to be at least 2.0.

Example 8 Preparation of a Colorless Mineral Film on a Substrate

A 5″.times.5″ plate of glass was washed with isopropanol to remove dirtand to clean the surface of the glass. Black electrical tape was placedaround the edges to form a container for the liquid binder solution.About 10 ml of the liquid binder of Ex. 4 was placed on the glass andthe liquid allowed to spread across the surface. The glass plate wasthen placed on a ceramic heater and the water is allowed to evaporate. Afilm of amorphous titanium oxide is produced. The film was clear andcolorless and adheres to the glass.

Example 9 Preparation of a Colorless Catalytic Film on a Substrate

Several 5″.times.5″ plates of glass were washed with isopropanol toremove the dirt and to clean the surface of the glass. Black electricaltape was placed around the edges of each to form a container for theliquid binder solution having a peroxide content of 0.110% to 0.08% asper Example 5. About 5 ml of the binder solution was placed on the glassand the liquid allowed to spread across the surface of the glass. Theglass plate was then placed on a ceramic heater and the water allowed toevaporate. An amorphous film covered the surface of the glass. The filmwas clear and colorless and adhered to the glass.

To determine the photo-catalytic activity of the coating, a photosensitive dye was brushed on the coated surface and allowed to dry. Forcomparison, the same dye was brushed on a plain glass plate. A dyedplate and a control plate were placed either 1] under a 15 watt UV lightsource or 2] in sunlight.

In sunlight, the color on the coated glass plate vanished within 2hours. Without the coating on a glass plate (control), the color tookmuch longer to become even slightly dimmed.

Under a 15-watt UV light source the color on the coated glass platevanished within about 12 hours. The plate without the coating was notaffected at all.

Example 10

Use of the Film as an Adhesive to Bind a Nanoparticle [or Larger] to aSubstrate

One kilogram of glass beads having a diameter of between 500 and 1000microns were washed with water. The glass beads were then mixed with 200gm. of isopropanol and 0.50 gm. of polyethylene oxide silane. 1538.46gm. of the solution of Example 4 was added to the bead mixture.

One hundred grams of rutile pigment, used to provide white opaquecoatings, was added to the solution with stirring. A mixing bladecontinuously stirred the batch as heat was applied to increase thetemperature to about 65° C. and the water allowed to evaporate. When thewater evaporated, a thin transparent clear coating with adhered rutilepigment is present on the surface of the glass spheres.

The pigmented glass spheres were spread out in a drying pan and placedin an oven at 100° C. for about three hours. At the end of the dryingtime the beads, with adhered pigment, were removed from the oven,cooled, packaged and stored.

1. A process for producing nanoparticles of a metal or metal compound ofless than 10 nanometers in size comprising forming an aqueous solutionof the metal peroxide having the formula M(OOH)_(x) where x is 2, 3, 4,or 6 from a hydroxide sol of the metal, diluting the solution to a metalperoxide concentration of between about 0.5% and about 0.85% by weightof the solution at a pH in the range of from about 4.0 to about 6.5,heating the solution to boiling for a period of from about 1 to about 4hours, cooling the solution, reheating the solution to boiling for aperiod of between about 1 and about 2 hours, cooling the solution, andreheating the solution to boiling until the peroxide concentration inthe solution is essentially zero and separating the nanoparticles. 2.The process of claim 1 where the metal peroxide is selected from thegroup consisting of peroxides of a metal of group III of the PeriodicTable.
 3. The process of claim 1 where the metal peroxide is selectedfrom the group consisting of peroxides of a metal of group II of thePeriodic Table.
 4. The process of claim 1 where the metal peroxide isselected from the group consisting of peroxides of scandium, lanthanum,yttrium, platinum, selenium, tin, vanadium, zirconium, hafnium, aluminumand iron.
 5. The process of claim 1 where the metal peroxide isTi(OOH)₄.
 6. The product of the process of claim
 1. 7. The product ofthe process of claim
 2. 8. The product of the process of claim
 3. 9. Theproduct of the process of claim
 4. 10. The product of the process ofclaim
 5. 11. A process for producing nanoparticles of a metal or metalcompound of less than 10 nanometers in size comprising forming anaqueous solution of a metal oxy peroxide of the formula MO(OOH)_(x)where x is 2, 3, 4, or 6, by decomposition of a solution of the metalperoxide having the formula M(OOH)_(y) where x is 2, 3, 4, or 6, whichwas formed from a hydroxide sol of the metal, diluting the solution ofthe metal oxy peroxide to a peroxide concentration of between about0.25% and about 0.425% by weight of the solution at a pH in the range offrom about 4.0 to about 6.5, heating the solution to boiling for aperiod of from about 1 to about 4 hours, cooling the solution to ambienttemperature, reheating the solution to boiling for a period of betweenabout 1 and about 2 hours, cooling the solution to ambient temperature,and reheating the solution to boiling until the peroxide concentrationin the solution is essentially zero and separating the nanoparticles.12. The process of claim 11 where the metal peroxide is selected fromthe group consisting of peroxides of a metal of group III of thePeriodic Table.
 13. The process of claim 11 where the metal peroxide isselected from the group consisting of peroxides of a metal of group IIof the Periodic Table.
 14. The process of claim 11 where the metalperoxide is selected from the group consisting of peroxides of scandium,lanthanum, yttrium, platinum, selenium tin, vanadium, zirconium,hafnium, aluminum and iron.
 15. The process of claim 11 where the metalperoxide is titanium peroxy acid.
 16. The product of the process ofclaim
 11. 17. The product of the process of claim
 12. 18. The product ofthe process of claim
 13. 19. The product of the process of claim
 15. 20.The product of the process of claim
 15. 21. A process for applying acolor-enhancing coating to a substrate comprising: (1) applying, to asubstrate, a composition comprising at least one color-enhancing agent,a binder material comprising the product of claim 6 and transparent ortranslucent glass beads having a refractive index between about 1.5 and2.5, and having a maximum diameter of up to about 20 microns; and (2)drying the composition to form a light-refracting, color-enhanced,translucent coating which envelops the color-enhancing agent and thetransparent or translucent beads which have a maximum diameter which isat least 10% less than the thickness of the cured coating layer andwhich refracts, scatters and dissipates applied light within the curedcoating.
 22. The process of claim 21 where the transparent ortranslucent beads are clear glass and have a refractive index of about1.9 to about 2.1.
 23. The process of claim 21 where the color-enhancingagent is at least one agent selected from the group consisting of dyes,pigments, metallic flakes, mica, opaque glass beads and holographicflakes.
 24. The process of to claim 21 where the transparent ortranslucent beads comprise a mixture of beads having differentrefractive indexes.
 25. The process of claim 21 where thecolor-enhancing agent comprises metallic flakes.
 26. The process ofclaim 21 where the transparent or translucent beads are colorless,transparent glass beads.
 27. The process of claim 21 where thecolor-enhancing agent comprises mica particles.
 28. The process of claim21 where the color-enhancing agent further comprises a colored pigmentor dye.
 29. A process for applying a water based light-refractive,color-enhancing coating to a surface, comprising the steps of (1)spraying the surface with a composition comprising (a) at least onecolor-enhancing agent from the group consisting of dyes, pigments,metallic flakes, mica, opaque glass beads, opaque glass particles ofrandom geometric shape and holographic flakes, and (b) transparent ortranslucent glass or plastic beads having a refractive index betweenabout 1.5 and 2.5, a maximum diameter which is up to about 20 micronsand is at least 10% less than the thickness of the coating, and (c) abinder material in accordance with claim 6; (2) heating the coatedsurface, if necessary to dry the composition to form a light-refracting,color-enhanced, translucent coating which envelops the color-enhancingagent and the glass or plastic beads and which substantially completelyrefracts, scatters and dissipates applied light within the coating. 30.The process of claim 29 where the color-enhancing agent is opaque glassbeads or opaque glass particles of random geometric shape and themaximum diameter of the beads is between about 10 and 20 microns. 31.The process according to claim 29 where the refractive index is betweenabout 1.9 and 2.1.
 32. Process according to claim 30 where the glassbeads comprise a mixture of beads having different refractive indexes.33. Process according to claim 29 where the composition comprises amixture of colorless, transparent glass beads and mica particles. 34.Process according to claim 31 where the composition further comprises acolored pigment or dye.
 35. A method of modifying the surface of asubstrate comprising coating the substrate with a pigment blendcomprising a plurality of glass particles selected from the groupconsisting of glass microspheres having a diameter less than about 50microns; and glass chips having a substantially random geometrical shapeand a particle size less than about 50 microns; wherein the glassparticles are at least partially coated with a colorless solution of ametal oxy peroxide of the formula MO(OOH)_(x) where x is 2, 3, 4, or 6manufactured by a process comprising forming an aqueous solution of ametal peroxide having the formula M(OOH)_(y), where y is 2, 3, 4, or 6where such solution is substantially free of other peroxides of themetal, diluting the solution to a metal peroxide concentration ofbetween about 0.5% and about 0.85% by weight of the solution at a pH inthe range of from about 4.0 to about 6.5, heating the solution toboiling for a period of from about 1 to about 4 hours, cooling thesolution, reheating the solution to boiling for a period of betweenabout 1 and about 2 hours, cooling the solution, reheating the solutionto boiling until the peroxide concentration in the solution is in therange of from about 12.5% to about 25% by weight of the initiallypresent metal peroxide, and cooling the resulting clear colorlesssolution.
 36. The method of claim 35, where the substrate is selectedfrom the group consisting of metal, ceramic, glass, asbestos, humanskin, leather, polymer, fabrics, wood, rubber, concrete, brick andasphalt.
 37. The method of claim 35, wherein the particle size is lessthan about 20 microns.
 38. The method of claim 35, where the glassparticles are selected from the group consisting of colorless, colored,luminescent, or phosphorescent glass particles.
 39. The method of claim38, where the luminescent glass particles are electroluminescent orchemiluminescent.
 40. The method of claim 35, where the glass particleshave an index of refraction between 1.5 and 2.5.
 41. The method of claim35, where the glass particles substantially inhibit transmission oflight in the ultraviolet spectrum.
 42. The method of claim 35, where theglass particles substantially inhibit transmission of light in theinfrared spectrum.
 43. A method of preventing degradation of a substrateby a topcoat applied thereto comprising coating the substrate with aclear, colorless solution of a metal oxy peroxide of the formulaMO(OOH)_(x) where x is 2, 3, 4, or 6 manufactured by a processcomprising forming an aqueous solution of a metal peroxide having theformula M(OOH)_(y), where y is 2, 3, 4, or 6 where such solution issubstantially free of other peroxides of the metal, diluting thesolution to a metal peroxide concentration of between about 0.5% andabout 0.85% by weight of the solution at a pH in the range of from about4.0 to about 6.5, heating the solution to boiling for a period of fromabout 1 to about 4 hours, cooling the solution, reheating the solutionto boiling for a period of between about 1 and about 2 hours, coolingthe solution, reheating the solution to boiling until the peroxideconcentration in the solution is in the range of from about 12.5% toabout 25% by weight of the initially present metal peroxide, cooling theresulting clear colorless solution applying the topcoat to suchsubstrate and drying the coated substrate.
 44. A process for increasingthe acid and alkali resistance of a substrate comprising coating thesubstrate with a clear, colorless solution of a metal oxy peroxide ofthe formula MO(OOH)_(x) where x is 2, 3, 4, or 6 manufactured by aprocess comprising forming an aqueous solution of a metal peroxidehaving the formula M(OOH)_(y), where y is 2, 3, 4, or 6 where suchsolution is substantially free of other peroxides of the metal, dilutingthe solution to a metal peroxide concentration of between about 0.5% andabout 0.85% by weight of the solution at a pH in the range of from about4.0 to about 6.5, heating the solution to boiling for a period of fromabout 1 to about 4 hours, cooling the solution, reheating the solutionto boiling for a period of between about 1 and about 2 hours, coolingthe solution, reheating the solution to boiling until the peroxideconcentration in the solution is in the range of from about 12.5% toabout 25% by weight of the initially present metal peroxide, cooling theresulting clear colorless solution, and drying the coated substrate. 45.An method of preventing the migration of labile ions from a substratecontaining labile ions comprising coating the substrate with a clear,colorless solution of a metal oxy peroxide of the formula MO(OOH)_(x)where x is 2, 3, 4, or 6 manufactured by a process comprising forming anaqueous solution of a metal peroxide having the formula M(OOH)_(y),where y is 2, 3, 4, or 6 where such solution is substantially free ofother peroxides of the metal, diluting the solution to a metal peroxideconcentration of between about 0.5% and about 0.85% by weight of thesolution at a pH in the range of from about 4.0 to about 6.5, heatingthe solution to boiling for a period of from about 1 to about 4 hours,cooling the solution, reheating the solution to boiling for a period ofbetween about 1 and about 2 hours, cooling the solution, reheating thesolution to boiling until the peroxide concentration in the solution isin the range of from about 12.5% to about 25% by weight of the initiallypresent metal peroxide, cooling the resulting clear colorless solution,and drying the coated substrate and drying the coated substrate.
 46. Themethod of claim 45 where the labile ions are sodium or potassium ions.